It is known that creatine and creatinine present in human serum or urine serve as indicators for the diagnosis of human diseases, particularly kidney disorders.
As an essential method for the chemical quantification of the above substances, the Jaffe method has been known up to now, but presents disadvantages such as troublesome procedures, low specificity, etc. Under these circumstances, a method for the enzymatic quantification of creatinine and/or creatine has been developed. In this method, creatinine is hydrolyzed by creatinine amidinohydrolase to form creatine which in turn is hydrolyzed into sarcosine and urea by creatine amidinohydrolase, and finally sarcosine oxidase is allowed to act on the resulting sarcosine so that the creatinine is quantitatively determined. Recently, this method is rapidly prevailing in clinical examination owing to the easy and simple procedures and higher specificity than that of the above chemical method.
The above creatine amidinohydrolase is known from e.g. Japanese Patent Publication No. 76,915/91.
However, such conventional creatine amidinohydrolase has disadvantages such as difficult purification at pH 8.5 or higher owing to its narrow stable pit range 4.5-8.5 and the long period of time required for the measurement of a sample owing to its high Km value.